Braden Blennerhassett, who flies for Air Frontier, said the snake appeared Tuesday about 20 minutes after he left Darwin, capital of the Northern Territory, the Australian Broadcasting Corp. reported.
No passengers were on board.
Blennerhassett radioed the Darwin airport requesting a snake handler: "I turned around and got it headed back towards Darwin there and said 'look, you're not going to believe this. I've got snakes on a plane.'"
By the time he landed, the snake had retreated into the plane's innards. Air Frontier director Geoffrey Hunt said traps have been set in the plane and it will not be used until the snake has been found.
Hunt said a snake-on-a-plane situation is unusual even for Australia's Top End, known for its aggressive reptiles.
"I have heard of crocodiles being loose in planes but not snakes," he said.